Z. Altun

Publications (5)6.02 Total impact

• Source

  Available from: ArXiv

  Article: Dielectronic Recombination of Fe XV Forming Fe XIV: Laboratory Measurements and Theoretical Calculations

  D. V. Lukić, M. Schnell, D. W. Savin, C. Brandau, E. W. Schmidt, S. Böhm, A. Müller, S. Schippers, M. Lestinsky, F. Sprenger, A. Wolf, Z. Altun, and N. R. Badnell
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  ABSTRACT: We have measured resonance strengths and energies for dielectronic recombination (DR) of Mg-like Fe XV forming Al-like Fe XIV via N = 3 → N' = 3 core excitations in the electron-ion collision energy range 0-45 eV. All measurements were carried out using the heavy-ion test storage ring at the Max Planck Institute for Nuclear Physics in Heidelberg, Germany. We have also carried out new multiconfiguration Breit-Pauli (MCBP) calculations using the AUTOSTRUCTURE code. For electron-ion collision energies 25 eV we find poor agreement between our experimental and theoretical resonance energies and strengths. From 25 to 42 eV we find good agreement between the two for resonance energies. But in this energy range the theoretical resonance strengths are ≈31% larger than the experimental results. This is larger than our estimated total experimental uncertainty in this energy range of ±26% (at a 90% confidence level). Above 42 eV the difference in the shape between the calculated and measured 3s3p(1P1)nl DR series limit we attribute partly to the nl dependence of the detection probabilities of high Rydberg states in the experiment. We have used our measurements, supplemented by our AUTOSTRUCTURE calculations, to produce a Maxwellian-averaged 3 → 3 DR rate coefficient for Fe XV forming Fe XIV. The resulting rate coefficient is estimated to be accurate to better than ±29% (at a 90% confidence level) for kBTe ≥ 1 eV. At temperatures of kBTe ≈ 2.5-15 eV, where Fe XV is predicted to form in photoionized plasmas, significant discrepancies are found between our experimentally derived rate coefficient and previously published theoretical results. Our new MCBP plasma rate coefficient is 19%-28% smaller than our experimental results over this temperature range.
  The Astrophysical Journal 12/2008; 664(2):1244. · 6.02 Impact Factor
• Source

  Available from: Dario Mitnik

  Article: Dielectronic recombination data for dynamic finite-density plasmas I. Goals and methodology

  N. R. Badnell, M. G. O'Mullane, H. P. Summers, Z. Altun, M. A. Bautista, J Colgan, T. W. Gorczyca, D. M. Mitnik, M. S. Pindzola, O. Zatsarinny
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  ABSTRACT: A programme is outlined for the assembly of a comprehensive dielectronic recombination database within the generalized collisional--radiative (GCR) framework. It is valid for modelling ions of elements in dynamic finite-density plasmas such as occur in transient astrophysical plasmas such as solar flares and in the divertors and high transport regions of magnetic fusion devices. The resolution and precision of the data are tuned to spectral analysis and so are sufficient for prediction of the dielectronic recombination contributions to individual spectral line emissivities. The fundamental data are structured according to the format prescriptions of the Atomic Data and Analysis Structure (ADAS) and the production of relevant GCR derived data for application is described and implemented following ADAS. The requirements on the dielectronic recombination database are reviewed and the new data are placed in context and evaluated with respect to older and more approximate treatments. Illustrative results validate the new high-resolution zero-density dielectronic recombination data in comparison with measurements made in heavy-ion storage rings utilizing an electron cooler. We also exemplify the role of the dielectronic data on GCR coefficient behaviour for some representative light and medium weight elements. Comment: 14 Pages, 9 Figures. Submitted to Astronomy & Astrophysics April 12, 2003
  04/2003;
• Article: Dielectronic recombination data for dynamic finite-density plasmas

  Z. Altun, A. Yumak, N. R. Badnell, J Colgan, M. S. Pindzola
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  ABSTRACT: A&A, 420, 775–781 (2004), DOI: 10.1051/0004-6361:20040964
  http://dx.doi.org/10.1051/0004-6361:20040003e.
• Article: Experimental dielectronic recombination rate coefficients for Na-like S VI and Na-like Ar VIII

  I. Orban, Z. Altun, A Källberg, A. Simonsson, G. Andler, A. Paál, M. Blom, P. Löfgren, S. Trotsenko, S. Böhm, R. Schuch
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  ABSTRACT: Aims. Absolute recombination rate coefficients for two astrophysically relevant Na-like ions are presented.Methods. Recombination rate coefficients of $\ion{S}{vi}$ and $\ion{Ar}{viii}$ are determined from merged-beam type experiments at the CRYRING electron cooler. Calculated rate coefficients are used to account for recombination into states that are field-ionized and therefore not detected in the experiment.Results. Dielectronic recombination rate coefficients were obtained over an energy range covering $\Delta\,n=0$ core excitations. For Na-like Ar a measurement was also performed over the $\Delta\,n=1$ type of resonances. In the low-energy part of the $\ion{Ar}{viii}$ spectrum, enhancements of more than one order of magnitude are observed as compared to the calculated radiative recombination. The plasma recombination rate coefficients of the two Na-like ions are compared with calculated results from the literature. In the $10^3{-}10^4$ K range, large discrepancies are observed between calculated plasma rate coefficients and our data. At higher temperatures, above $10^{5}$ K, in the case of both ions our data is 30% higher than two calculated plasma rate coefficients, other data from the literature having even lower values.Conclusions. Discrepancies below $10^4$ K show that at such temperatures even state-of-the-art calculations yield plasma rate coefficients that have large uncertainties. The main reason for these uncertainties are the contributions from low-energy resonances, which are difficult to calculate accurately.
  http://dx.doi.org/10.1051/0004-6361/200911799.
• Source

  Available from: Stefan Schippers

  Article: Dielectronic Recombination In Active Galactic Nuclei

  D. V. Lukic, M. Schnell, D. W. Savin, Z. Altun, N. Badnell, C. Brandau, E. W. Schmidt, A. Müller, S. Schippers, F. Sprenger, M. Lestinsky, A. Wolf
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  ABSTRACT: XMM-Newton and Chandra observations of active galactic nuclei (AGN) show rich spectra of X-ray absorption lines. These observations have detected a broad unresolved transition array (UTA) between ˜ 15-17 Å. This is attributed to inner-shell photoexcitation of M-shell iron ions. Modeling these UTA features is currently limited by uncertainties in the low-temperature dielectronic recombination (DR) data for M-shell iron. In order to resolve this issue, and to provide reliable iron M-shell DR data for plasma modeling, we are carrying out a series of laboratory measurements using the heavy-ion Test Storage Ring (TSR) at the Max-Plank-Institute for Nuclear Physics in Heidelberg, Germany. Currently, laboratory measurements of low temperature DR can only be performed at storage rings. We use the DR data obtained at TSR, to calculate rate coefficients for plasma modeling and to benchmark theoretical DR calculations. Here we report our recent experimental results for DR of Fe XIV forming Fe XIII.
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